Municipal fluid distribution systems include water mains, gas mains and customer service lines connected to the mains for supplying individual customers. Most of the service lines are installed after the main line is in service. Therefore, a need exists to install service lines while the main conduit is carrying fluid under pressure.
Fittings for connecting service lines to mains usually incorporate a valve therein called a corporation stop valve, and the assembly of the valve and fitting is called a corporation stop assembly. They may, however, also be called service tees, elbows or straight transition fittings. In the past, where such fittings have been used with cast iron or steel pipe the inlet portion of the fitting was made with a tapered thread that cooperated with threads in a tapped hole in the main. With the increased popularity of plastic pipe made of polyethylene (PE), holes could be tapped but the threaded engagement of polyethylene parts often resulted in a leaking connection.
In view of this, service clamps, which incorporate two metal saddle parts for encircling the main pipe, are commonly used in making connections on main pipes of polyethylene. In these service clamps, one saddle part carries a branch pipe extension with a through bore that may be at least partially threaded for receiving a tapping tool to form a hole in the main pipe. The cutting member of the tapping tool is typically inserted through a valve attached to the bore of the branch pipe extension to allow removal of the tapping tool on pressurized systems without the escape of fluid from the main. Each saddle part carries a bolt or screw on opposite sides of the main pipe for uniformly clamping the assembly together. The main disadvantage of this service clamp is that it cannot be assembled quickly or easily about a main pipe, especially when using nuts with bolts for drawing the two saddle parts together is necessary. Accordingly, it requires considerable manipulation of the parts to insert bolts or screws into the tapped holes of the saddle parts while in the confines of a trench where the main pipe is found, and where adequate space for convenient assembly is lacking.
Self tapping saddle tee pipe fittings that are made of plastic material similar to the plastic used for the main pipe, have also come into widespread use. In this instance the fitting includes a saddle portion provided with an arcuate shaped surface complementary to the exterior surface of the main pipe. These fittings can be permanently attached to the main plastic pipe by solvent welding, heat-fusion, electro-fusion, where abutting thermoplastic materials are brought to fusion temperature by electrically heating wires embedded in the thermoplastic material, or other bonding operation that permanently seals the saddle portion to the main pipe. The coupon cutter is provided with exterior threads that cooperate with the threads of the through bore for advancing the cutter. A self tapping saddle tee of the type described above is more fully described with reference to FIG. 2, and fusion techniques discussed at col. 1, lines 40-48, of U.S. Pat. No. 5,076,318, incorporated herein by reference.
While these self tapping saddle tees that can be sidewall fused to a polyethylene main pipe have found widespread use, several problems still exist, especially in making connections to thick wall, large diameter mains. For example the saddle tees, which have service outlets at 90.degree. with respect to the through bore, are most conveniently installed on top of the main. This results in the service outlet having a 90.degree. angle from the vertical. Installation contractors, however, prefer installing branch service lines having outlets extending from the lowest stress point on the main pipe, which is a 45.degree. angle from the vertical. Another problem that limits use of the selftapping saddle tees is that in most instances the main pipe must be of relatively thin wall construction. Other problems arise in that self tapping tees are only available with 3/4 inch and 1 inch outlet sizes for use on 3 to 12 inch (IPS/CTS) main pipes. A further problem is that while polyethylene service lines can be either butt fused or attached with a mechanical coupling to the outlet of the self tapping tee, a copper service must be attached with a mechanical coupling. Yet another problem arises in that such self tap-tees allow entrapment air to enter the customers' service line.
Accordingly, it is an object of this invention to provide a corporation stop assembly that promotes use of polyethylene pipe for municipal distribution systems.
Another object is to reduce labor costs for installing corporation stop valves.
A more specific object of the present invention is to simplify installation of branch pipes extending from the main pipe at a 45.degree. angle from vertical.
Yet another object is to provide a corporation stop assembly for making a zero-leak-rate monolithic joint with a main pipe.
Another object is to provide a corporation stop assembly that advantageously replaces strap-on saddle and threaded corporation stop assemblies used on polyethylene pipe.
Yet another object of this invention is to provide a valve outlet fitting that is compatible with both polyethylene service lines and copper service lines.
Still another object is to hot tap a polyethylene pipe having a wall thickness of two inches.